Transglutaminases are enzymes which catalyze an acyl transfer reaction of a .gamma.-carboxyamide group of a glutamine residue in a peptide or protein chain.
The transglutaminases form intramolecular or intermolecular .epsilon.-(.gamma.-Glu)-Lys cross-linking wherein the .epsilon.-amino group of the lysine residue in the protein serves as the acyl receptor. When water functions as the acyl receptor, the transglutaminases catalyze deamination of glutamine residues to form glutamic acid residues.
The protein gelation products obtained utilizing the transglutaminases according to the present invention are used as yoghurt, jelly, cheese, gel cosmetics, etc., including conventional gel foodstuffs and gel cosmetics.
In the animal-derived transglutaminase, there are hitherto known, the transglutaminases which are widely distributed in, for example, liver of the guinea pig (Connellan, et al., Journal of Biological Chemistry, Vol. 246, No. 4, pages 1093-1098 (1971)) and mammal organs and blood (Folk et al., Advances in Enzymology, Vol. 38, pages 109-191 (1973) and Folk et al., Advances in Protein Chemistry, Vol. 31, page 1-133 (1977)) and characteristics of the enzymes have been investigated.
However, application of the animal-derived transglutaminase to industry, particularly, the process for producing protein gelation products involves defects as described below.
It is difficult to obtain animal-derived transglutaminases at low cost and in large quantities. Also, there is the restriction that at least 1 unit of this expensive enzyme and at least 2.0 wt. % of a substrate protein concentration per 1 g of substrate protein are required for gelation. Further, the animal-derived transglutaminase is calcium (Ca.sup.2+)-dependent so that its application is limited.
Because of the foregoing defects, processes for producing gelation products using animal-derived transglutaminases are impractical.
Also, in view of the above difficulties of applying animal-derived transglutaminases in an industrial setting, a microorganism-derived transglutaminase which is produced by the genus Streptoverticillium has previously been proposed by the present inventors in European Patent Publication No. 0 379 606Al.